Explosion in Gasoil Hydro-Treatment Unit During Start-Up
On a cold morning, the gasoil hydro-treatement unit was being brought back on line after being out of service to repair a governor problem on the recycle gas compressor. Several upset trips had occurred in the previous month but these were not seen to have any direct bearing on the operation of he hydrogen heaters or the unit as a whole, Temperature at the coil outlet of both heaters was at least 100 degrees C lower than normal since the unit was in a start up mode. The reactor circuit was at full operating pressure while hydrogen was recycled via a compressor. A violent explosion suddenly occurred within one of the heaters and a loud noise accompanied by shock was felt across the plant site. For one half hour, flames emitted from the top of the stack was felt from the top of the stack. Operators tried to isolate the heater from known fuel sources but they were unable to access the isolation valves. Fortunately, no injuries were sustained as a result of the initial explosion or the fire that followed. The fire was finally extinguished with little damage occurring outside the heater shell. In fact, the force of the explosion did not even dislodge the explosion panels on the furnace.
Event Date
November 30, 1978
Record Quality Indicator
Region / Country
Event Initiating System
Classification of the Physical Effects
Nature of the Consequences
Cause Comments
The accident was believed to be caused by an improper design and failure to conduct pre-start-up safety reviews prior to a routine start-up.
Facility Information
Application Type
Application
Specific Application Supply Chain Stage
Components Involved
recycle gas compressor
Location Type
Location description
Industrial Area
Pre-event Summary
On a cold morning in late 1978, the gasoil hydrotreater was being brought back on line after being out of service to repair a governor problem on the recycle gas compressor. Several upset trips had occurred in the previous month but these were not seen to have any direct bearing on the operation of he hydrogen heaters or the unit as a whole, Temperature at the coil outlet of both heaters was at least 100 degrees C lower than normal since the unit was in a start-up mode. The reactor circuit was at full operating pressure while hydrogen was recycled via a compressor.
Lessons Learned
Lessons Learned
It is important to prepare more effective furnace designs. However, as long as designs include hardware such as piping, there is some potential for valves and ttings to be wrongly positioned. There is no procedure that can dene all the requirements for a good circuit design. On the other hand, if process designs are thoroughly reviewed under a wide range of conditions, potential failures should be picked up and addressed. New designs need to consider normal operating conditions as well as those associated with start-up, shutdown and recovery from upset. We also learned the importance of monitoring especially during start-up periods. Data analysis after the fact showed a high stack temperature, an anomaly which should have indicated afterburning or process leakage. Start-up procedures need to include diagnostics for dealing with unusual conditions. Prior to starting up, the unit should have been thoroughly inspected to ensure that it was suitable for commissioning. Unscheduled outages can leave equipment in an intermediate state (partly lled with inventory) which does not coincide with normal start-up procedures. There may sometimes be a tendency to bypass procedures in order to get equipment back on line. Upset conditions and temporary feed outages, for whatever reason, must receive priority attention from operations and technical staff.
Event Nature
Emergency Action
Unknown
Detonation
No
Deflagration
No
High Pressure Explosion
No
High Voltage Explosion
No
Source Category
References
References
Brian D. Kelly,
Investigation of a hydrogen heater explosion,
Journal of Loss Prevention in the Process Industries 11 (1998) 257–259